An Improved Schottky Diode

R. J. N.

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The conventional Schottky barrier diode (which does not inject minority carriers) is capable of switching times less than 0.1 nanosecond. An improved version has been developed by M. P. Lepselter and S. M. Sze at the Bell Telephone Semiconductor Device Laboratory (Bell Laboratories Record 1967, 45 (Nov.), 340). The introduction of a guard ring eliminates “edge effect”, giving a breakdown voltage close to the theoretical limit, while the use of a very clean junction between the n-type silicon semiconductor and a layer of platinum silicide provides an almost ideal forward current-voltage characteristic.

The n-type silicon substrate is cleaned by a glow discharge in which gas ions remove impurities by bombardment. Without removal from the vacuum chamber a smooth layer of platinum is then sputtered on. The result is a layer of uncontaminated platinum silicide with a near-perfect interface to the n-type silicon. Successively, a guard-ring of p-type silicon is formed, a silicon dioxide layer deposited, channels of access etched, and gold beam leads applied.

Platinum silicide is a very stable compound, highly resistant to corrosion and able to form a low-resistance contact. In other related applications the silicide layer receives a deposit of titanium followed by a platinum layer. The titanium layer bonds strongly to the silicon dioxide insulating layer, which it improves by absorbing impurities. The further platinum layer is required to form a strong bond with the gold leads, and also to prevent gold/titanium reactions.